Glass, which is a relatively inexpensive insulator, is widely used as a material for solar cell substrates. However, glass is brittle. Therefore, it is difficult to continuously manufacture a large number of glass solar cell substrates on which an absorber layer formed.
Therefore, solar cell substrates made of a metal sheet (for example, a stainless steel sheet or the like) which can be mass-manufactured and which is more inexpensive than glass are under development. However, the metal sheet is a conductive material. Therefore, in order to use the metal sheet for a substrate for integrated solar cells, an insulating layer needs to be formed on a surface thereof. Alternatively, solar cells attached to power-collecting-surfaced electrodes are connected to each other like silicon solar cells and can be used as a grid type.
For example, Patent Literatures 1 and 2 disclose an insulating sheet including an alumina coating formed on a smooth surface of a stainless steel sheet. When a back-contact including a Mo layer is formed on the insulating sheet and a coating of Cu(In1-xGax)Se2 is formed thereon as an absorber layer, heat treatment for growing crystals of Cu(In1-xGax)Se2 is performed and the resultant insulating sheet is used as an integrated solar cell substrate, whereby production costs can be reduced as compared to a glass solar cell substrate.
Alternatively, in the case of being used as a grid-type solar cell substrate, when a surface of a stainless steel sheet is smoothed, a back-contact made of a Mo layer is formed thereon, and a coating of Cu(In1-xGax)Se2 is formed thereon as an absorber layer, heat treatment for growing crystals of Cu(In1-xGax)Se2 is performed, whereby a solar cell substrate is formed. Incidentally, Cu(In1-xGax)Se2 refers to a substance which is a mixed crystal of Cu(In)Se2 and Cu(Ga)Se2 and which is referred to as CIGS.
In these solar cell substrates using the stainless steel sheets (that is, solar cell substrates made of stainless steel sheet), when insulating layer or the back-contacts are formed, there is a case where Cr layers or the like referred to as barrier layers are formed as underlayers in advance.
In this case, the insulating coatings, the back-contacts, and the absorber layers other than the barrier layers are formed in substantially the same way as above.